{"id":75,"date":"2010-05-05T13:01:53","date_gmt":"2010-05-05T17:01:53","guid":{"rendered":"https:\/\/extension.umaine.edu\/blueberries\/?page_id=75"},"modified":"2025-09-10T11:24:20","modified_gmt":"2025-09-10T15:24:20","slug":"fertilizing-with-nitrogen-phosphorus","status":"publish","type":"page","link":"https:\/\/extension.umaine.edu\/blueberries\/resources\/nutrient-management\/fertilizing-with-nitrogen-phosphorus\/","title":{"rendered":"225-Fertilizing with Nitrogen and Phosphorus"},"content":{"rendered":"

Fact Sheet No. 225, UMaine Extension No. 2094<\/strong><\/p>\n

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Prepared by David E. Yarborough, Extension Blueberry Specialist, and John M. Smagula, Emeritus Professor of Horticulture, The University of Maine, Orono, ME 04469. Revised January 2013.<\/em><\/p>\n

Introduction<\/strong><\/h3>\n

Before preemergence herbicides were available blueberry fields were fertilized with only small amounts of nitrogen fertilizer.\u00a0 Growers didn’t want to help weeds grow since weeds also respond to fertilizer. Weeds compete for light, moisture, and nutrients and will lower blueberry yields.\u00a0 However, when growers used herbicides to control weeds, extra fertilizer did not increase yields.\u00a0 In this case, there were enough nutrients in the soil for blueberry production. Recent research indicates higher levels of fertilizer will improve yields if other limiting factors such as having adequate pollination, protection from disease and insect damage and adequate moisture from irrigation are provided see Wild Blueberry Fact Sheet PDF on the\u00a0Improving Your Wild Blueberry Yields page<\/a>.<\/p>\n

Based on our surveys, most Maine blueberry fields have adequate levels of leaf nitrogen and phosphorus but the levels needed have been increased compared to the leaf nutrient standards set by University of Maine researcher Trevett in 1972. The new standards are found on the\u00a0Wild Blueberry Fact Sheet No. 223, Interpreting your leaf analysis results<\/em><\/a>.<\/p>\n

Soil samples show that soil nutrient levels aren’t always the same as leaf nutrient levels.\u00a0 For example, in some fields where soil phosphorus was low, leaf phosphorus was not low.\u00a0 This is why we don’t make fertilizer recommendations based on soil samples. To find out leaf nutrient levels, you need to sample your non-bearing fields at the tip-dieback stage of growth.\u00a0 Refer to the\u00a0Wild Blueberry Fact Sheet No. 222, Leaf and Soil Sampling Procedures<\/em><\/a> for detailed methods on leaf and soil sampling.<\/p>\n

Results of Fertilizer Experiments<\/strong><\/h3>\n

Researchers have experimented with Diammonium phosphate (DAP) and phosphorus (P) fertilizers since 1987 to determine the relationship between fertilizers, leaf nutrients, and blueberry yield. The top graph shows results from one study on eight fields over two years. The bottom graph gives data for one field over four years.<\/p>\n

The top graph shows that leaf phosphorus (P) will increase above the standard of 0.125 percent leaf P with DAP fertilization but will begin to level off at 200 lb\/a DAP. These lines represent an average response. In other words, some fields had higher or lower leaf P and yields. Studies with P alone showed the same trend, but yields were lower. In this case, Nitrogen (N) was necessary to get a higher yield. New levels developed by Santiago in 2011 indicate that with more intensive practices that higher yields may be obtained than in the past so the recommendations of leaf levels and fertilizer application have been adjusted to reflect the greater demands on the plant.<\/p>\n

\"Effect<\/a>
Effect of DAP Fertilization<\/figcaption><\/figure>\n

The graph to the right also illustrates that leaf P and yield will increase with DAP. It also shows that an increase in leaf P does not guarantee an increase in yield: the leaf P was higher in 1991 than 1989, but the yield was lower in 1992 versus 1990. This tells us that factors other than fertilizer have an effect on yield. Having a sufficient number of bees for pollination, adequate moisture and winter injury or frost will affect your yield.<\/p>\n